As King bloom approaches in many Wisconsin orchards, fire blight prevention efforts are underway. According to NEWA, fire blight risks currently vary from region to region in Wisconsin, so please consult models for your area to evaluate risks and make informed decisions.

Streptomycin is still the best option for fire blight control during bloom. In Wisconsin, the fire blight pathogen shows sensitivity to streptomycin, with no reported cases of resistance. Streptomycin exhibits partial systemic properties, offering some post-infection activity. Applying streptomycin 2 to 4 days before rain events is highly effective in controlling blossom blight. A single application offers approximately 48 hours (about 2 days) of protection. Resistance management strategies include limiting streptomycin to two to three applications per season, only during bloom, and avoiding use during the summer for shoot blight control.

For shoot blight control, Apogee is initially applied during king bloom petal fall. It typically takes around 10-14 days for growth inhibition to become noticeable. While one application is often sufficient to control fire blight development, additional applications are allowed and could be advantageous for highly susceptible varieties or very vigorous trees. Apogee was recently given a Section 2(ee) recommendation in Wisconsin to allow a first application of Apogee between the pink stage of flower development and 1 to 3 inches of new growth. Apogee can be included in streptomycin programs to prevent shoot blight post-petal fall.

If utilizing copper, applications should be made during fast-drying conditions and should target non-bearing plants, as there is a risk of russeting associated with copper applications. Utilizing a combination of Cueva (copper) and Double Nickel (Bacillus-based biocontrol) has shown promise for managing shoot blight when applied weekly, starting at King Bloom petal fall. Soluble coppers ensure that all copper ions are present upon application to quickly kill bacteria.

Biologicals such as Lifegard demonstrate highest efficacy when applied before initial infections can occur. To effectively control fire blight, application during early bloom stages is recommended. However, applying it during late bloom or post-bloom stages may still help decrease the occurrence of shoot blight. Other products such as Regalia and Blossom Protect provide some control when applied during bloom, and typically work best when integrated in conventional programs.

Utilize weather-driven predictive models such as Maryblyt and Cougar Blight to determine the optimal timing for applying protective bactericides.  Avoid applying bactericides too early, because it typically takes a couple of days for the fire blight pathogen to build up once flowers are open. If flower opening occurs rapidly, consider shortening application intervals accordingly.

Apple scab protection. With cooler temperatures, we are looking at predicted infection events through Thursday and Friday in some parts of Wisconsin according to the NEWA models, check the model in your area.

For additional articles on fire blight published in the WI Fruit News:

• https://fruit.wisc.edu/2022/05/05/fire-blight-and-the-season-ahead/
• https://fruit.wisc.edu/2023/06/29/fire-blight-pruning-management-recent-updates/

This article was posted in Apples, Disease and tagged Apple Scab, Apples, bloom time, disease, disease control, Fire Blight, Leslie Holland.